This invention relates to elbows for use in systems for transporting fluent materials and in particular to a short radius elbow for use in a system for pneumatically conveying solid particulate material such as fly ash, cement and similar abrasive materials.
Prior to the present invention, it was common practice to utilize long radius turns in pneumatic conveying systems. It was believed that these long radius turns reduced wear on the conveying pipeline as well as minimizing pressure drop. It was also known prior to the present invention to utilize short radius turns or elbows insystems for conveying fluent materials and employ a thickened or stepped wear resistant surface on the inside of the elbow to prolong the life of the elbow. With prior designs, the impact steps are located primarily in the outlet leg only. With this type of wear resistant elbow, the material often impacts the stepped wear resistant portion and is re-entrained by high level fluid energy in the downstream leg of unprotected portions of the following conveying pipe.
It has been discovered by the present invention that by placing the wear resistant steps symmetrically toward both the inlet leg and the outlet leg, an improved wear resistant elbow is achieved in that the primary impact of the abrasive material being conveyed is absorbed by the wear resistant section of the elbow, that there is early rebound of material back to the turning air stream and less material build up in the area upstream. This early rebound of material means that the wear caused by material being turned is absorbed by the protected portion of elbow and less in the following pipe as in the prior art.